Steel containing chromium molybdenum and nickel



Dec. 15, 1970 STEEL CONTAINING CHRQMIUM MQLYBDENUM AND N'IdKEL C. G.BIEBER ETAL Filed 3111 27, 1967 1 6 F 1 l I Y K A/ B 6 0 EL Q W04YBDE/VU/V z INVENTORS.

3,547,625 STEEL CONTAINING CHROMIUM MOLYBDENUM AND NICKEL ClarenceGeorge Bieber, Sutfern, N.Y., and Roger Allen Covert, Middletown, N.J.,assiguors to The International Nickel Company, Inc., New York, N.Y., acorporation of Delaware Continuation-impart of application Ser. No.574,995, Aug. 25, 1966. This application July 27, 1967, Ser. No. 656,542

Int. Cl. C22c 39/20 US. Cl. 75--128 11 Claims ABSTRACT OF THE DISCLOSUREIron-base alloys containing, among other constituents, interrelatedamounts of nickel, molybdenum, and chromium offer a relatively highdegree of resistance to various forms of corrosion in either or both theannealed and cold worked conditions. Alloys are also hot and coldworkable and exhibit high tensile strength.

This is a continuation-in-part of application Ser. No. 574,995 filedAug. 25, 1966.

The present invention relates to corrosion resistant alloys,particularly to iron-nickel alloys of novel composition and which are ofcomparatively low cost, both hot and cold workable, and which manifestenhanced resistance to corrosion, including crevice, pitting,intergranular and stress corrosion cracking, especially in chloridmedia, notably marine environments such as sea water.

As is generally well known, there has been a substantial increase overthe years in the tonnage of metals and alloys used in resisting thecorrosive effects of chlorides, including salt solutions, stronglyoxidizing chloride solutions and marine environments. Commercialinterest has been particularly expanding in respect of marineapplications and this has been undoubtedly spurred by recent activitiesin oifshore drilling, desalinization, undersea mining, etc. However,unless improved and more corrosion resistant materials are developed,the heavy toll in metal damage inflicted by corrosion will continue toincrease. It is perhaps interesting to reflect that a recent reportindicates the overall loss exacted by corrosion is currently on theorder of about five billion dollars annually. Such an economic burdenself-explains the necessity of at least curtailing this trend.

A number of metals and alloys are currently being used or have beenproposed for marine application, including the austenitic stainlesssteels, carbon and alloy steels, copper and copper alloys includingvarious brasses, nickel alloys, titanium and alloys thereof, etc.However, depending upon intended purpose, such materials suffer from oneor more drawbacks. The austenitic stainless steels, e.g., AISI, 304,310, 316, are readily workable and of reasonably low cost but do notexhibit superior resistance to crevice corrosion. This applies to aneven greater extent concerning the carbon and low alloy steels. Copperalloys manifest a propensity to pit when immersed in sta nant sea wateror when the rate of flow is less than about five feet per second (alsotrue of austenitic stainless steels). This is not an unusual occurrencesince it is known that as sea water velocity increases, fouling andpitting diminish in respect of many (although not all) materials.Certain nickel-base alloys have been used rather extensively. One of themost popular of such alloys contains about 17% chromium, 16% molybdenumand 4% tungsten but is costly and, at best, diificultly workable andusually requires several intermediate annealing treatments during theworking cycle, a factor contributing to increased cost. Titanium andtitanium alloys suffer from United States Patent m Patented Dec. 15,1970 the shortcoming of being of comparatively high cost andcatastrophic corrosion has been experienced with certain titaniumalloys.

The general problem is somewhat complicated by the fact that whilecertain applications require alloys which must resist chloride attack inthe annealed condition, for other applications, e.g., marine cable(rope), it is more important that alloys manifest both high strength andexceptional resistance to chloride corrodents in the cold rolledcondition. The ultimate, of course, would be to have available low costalloys highly satisfactory in either condition, thus obviating concernas to which condition an alloy behaves more favorably. Each of theseobjectives is accomplished in accordance with the instance inventionwhich is addressed to the specific problem of providing low cost, hotand cold workable alloys which exhibit markedly improved resistance tocrevice, pitting, intergranular and stress corrosion cracking inoxidizing chloride media, marine environments, etc.

It has now been discovered that the objectives abovediscussed can bereadily achieved with certain alloys containing special and correlatedamounts of iron, nickel, chromium, molybdenum, and controlled amounts ofaluminum, titanium, calcium, carbon, silicon, manganese, etc.

It is an object of the invention to provide improvediron-nickel-chromium-molybdenum alloys of novel composition.

Another object of the invention is to provide noveliron-nickel-chromium-molybdenum alloys of enhanced resistance tocorrosive media, particularly chloride environments such as marineatmospheres, sea water, salt solutions, strongly oxidizing chloridesolutions, etc.

It is a further object of the invention to provide new low cost, hot andcold workable corrosion resistant alloys.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the accompanying drawing in whichthere is depicted a chart in respect of nickel and molybdenum contentspertaining to alloys within the invention as herein more fullydescribed.

Generally speaking and in accordance with the present invention, alloyscontemplated herein contain (in percent by weight) about 20% to 40%nickel, about 6% to 12% molybdenum, about 14% to 21% chromium, thechromium content being at least about 18% and advantageously at least18.5% when the molybdenum content is not greater than about 6.5% or 7%and not exceeding 20% and preferably not exceeding 19% when themolybdenum content is from 10% to 12%, up to 0.2% carbon, up to 0.5%silicon, up to 1% but beneficially not more than 0.5% manganese, the sumof the silicon plus manganese not exceeding about 1.25%, up to 0.7%titanium, up to 0.7% aluminum, up to about 0.15% calcium, up to 12%cobalt, and the balance essentially iron, the iron constituting at least30% of the alloys. In consistently achieving good hot workabilitycharacteristics, the alloys advantageously contain titanium or aluminum(most beneficially both) in amounts of from 0.05% to 0.6% each, e.g.,0.15% to 0.5%. Further, it is most preferred and desirable that thealloys contain calcium, e.g., 0.001% or 0.01% to 0.15% calcium, inconsistently achieving highly satisfactory results. The theory whichmight explain the role of calcium is not completely understood, butapart from other possible benefits, it has been found that calciummarkedly influences and enhances resistance to crevice corrosion in boththe annealed and cold worked conditions, particularly the latter andparticularly with regard to alloys containing not more than about 8%molybdenum, e.g., 7.5% molybdenum, or lower. Calcium must be presentwhen the molybdenum content of the alloys is not greater than about 7.5%or 8%; otherwise, crevice corrosion resistance is adversely affectedeven inthe annealed condition.

Other constituents which can be present in the alloys include thefollowing: up to 2%, e.g., up to 0.5% or 1%, columbium, up to 1%vanadium, up to 1% copper, up to 1% tungsten and up to 2% tantalum.However, elements such as phosphorus, sulfur, oxygen, nitrogen, and thelike should be kept at low levels consistent with good commercialpractice. Sulfur is deemed particularly detrimental and particular careshould be exercised in this regard. It is thought that one of theattributes of calcium is that it counteracts the deleterious effects ofsulfur. Nitrogen should be maintained below about 0.03%, preferablybelow about 0.01%.

In carrying the invention into practice, the alloys should contain atleast 20% nickel. With nickel levels lower by an appreciable extent,corrosion resistance in marine and other environments is not onlyunsatisfactory but there is the added danger of forming delta ferrite.If present in an excessive although relatively low amount, delta ferritepromotes or potently contributes to embrittlement problems wherebyworkability is, at best, impaired. In this connection and in accordancewith the invention, the alloys should be substantially austenitic(single phase) and devoid of detrimental delta ferrite and/or otherdeleterious phases such as sigma.

Further, consistently highly satisfactory results do not always obtaineven with nickel contents of, say, about 20% to 23%. For example, whenthe content of molybdenum in the alloys is above about 9.5%, e.g., andup to 12%, it has been found that unless the nickel content exceedsabout 23%, both hot and cold workability are rendered more difficultsuch that intermediate annealing may be required and this increasescost. Moreover, at a nickel level of less than about 23%, resistance tocrevice corrosion, especially in respect of alloys in the cold rolledcondition, is inferior when both the molybdenum and chromium are at thelow end of their respective ranges. When the nickel content is as low asand the molybdenum content is from 6% to about 6.5%, the alloys shouldcontain about 18% or more of chromium, e.g., 18.5%, as indicated aboveherein. Generally speaking, at a molybdenum level above about 6.5% toabout 7.5%, a chromium content of about 17% and upwards should be usedwith nickel contents as low as 20%. At about 7.5% to 8% molybdenum,about 15.5% or 16% chromium and above can be used with such low (as wellas higher) nickel contents. It is beneficial, however, for an optimumcombination of resistance to crevice corrosion coupled with goodworkability, that the alloys contain at least 23% and moreadvantageously at least 24% or nickel.

In respect of the higher end of the nickel range, to wit, to nickel, aparticularly noteworthy feature of the invention stems from the factthat not only is resistance to crevice and pitting corrosion and thelike markedly good in chloride media but resistance to stress corrosioncracking is excellent. As will be illustrated herein, this obtains notonly in marine environments, sea water, but most significantly when thealloys are exposed to the extreme aggressive attack so characteristic ofboiling magnesium chloride. Alloys resistant to stress corrosioncracking should contain, in addition to 35 to 40% nickel, above about9%, e.g., 9.5%, and up to 12% molybdenum and about 14% to not more thanabout 19% chromium, the balance of the composition being in accordancewith that given before herein. Up to 10% cobalt can be used to replacean equivalent amount of nickel. Where outstanding resistance to creviceand pitting corrosion coupled with resistance to stress corrosioncracking is required, it is beneficial that the alloys contain, inaddition to a nickel plus cobalt content of about 35% to 40%, about 10%to 12% molybdenum and about 14% or 15% to 18% chromium.

Low molybdenum contents result in inferior resistance to crevicecorrosion. For example, molybdenum contents of 4% are markedly poor.Too, as will be shown herein, an amount of molybdenum of, say, 6% isquite unacceptable should the chromium content be on the low side, e.g.,14% to 17%. It is most advantageous that at least 8% molybdenum bepresent in the allows and even then satisfactory results will notconsistently obtain unless the molybdenum, nickel, and also the chromiumcontents are correlated. In this regard, it is not a question of usinghigh nickel contents to attain a desired degree of resistance.Increasing the amount of nickel beyond about 27% or 28% has been foundto result in lower crevice corrosion resistance at molybdenum levels ofabout 7%. But by using 8% or more of molybdenum particularly withchromium contents of at least 17%, highly satisfactory results can beobtained at higher nickel levels. The correlation between nickel andmolybdenum is represented by the accompanying drawing. It should bepointed out that with respect to the area, ABCLA, an area encompassing afair number of alloys at nickel percentages above 28% but amounts ofmolybdenum of less than 8%, the chromium content for such compositionsshould be about 18% or more.

In addition and subject to the foregoing, where resistance to stresscorrosion cracking in potently aggressive agents such as boilingmagnesium chloride is not necessary, and thus a nickel minimum of 35% isnot required, highly satisfactory results are attained when themolybdenum and nickel contents are interrelated to represent a pointwithin the area ABCDEFA of the accompanying drawing, the chromiumcontent of the alloys advantageously being from 14% or 15% to 20%, e.g.17% to 20%. Alloys containing from about 15% to 20% chromium and havingmolybdenum and nickel contents representing a point falling within thearea BGHJKB, and particularly within the area GHJKG, are deemedespecially attractive commercially since they would be the mosteconomical, are readily amenable to both hot and cold working, andprovide good resistance to crevice corrosion in both the hot and coldworked conditions.

In addition to what has been said before herein in respect of chromiumand while it contributes to resisting corrosive attack, excessiveamounts thereof can lead to poor results, particularly by promoting amultiple phase structure. This, in turn, would bring about adverseconsequences. A chromium content of, say, 22%, part from beingunnecessary, is particularly undesirable to molybdenum levels of 9% andabove. Accordingly, when the molybdenum content is from about 9.5% or10% to 12%, the chromium content, as indicated before herein, should notexceed 20% and advantageously does not exceed about 19%.

Careful control must be exercised with regard to silicon and manganese.Silicon in appreciable quantities, e.g., 1% or 2%, is notablyundesirable by reason of the fact that it impairs hot workability andweldability. Manganese in comparatively high amounts, e.g., 1.5% to 2%,also significantly impairs corrosion resistance. As indicated aboveherein, it is preferred that the total silicon plus manganese contentnot exceed 1.25%. Advantageously, the silicon content should not exceed0.25% and the total silicon plus manganese should not exceed about0.75%.

Although the amount of carbon in the alloys can be as high as 0.2%,carbon somewhat in excess of 0.1%, e.g., 0.15%, results in diminishingcrevice corrosion resistance in otherwise outstanding alloys. Inachieving both good crevice corrosion resistance and resistance tointergranular corrosion, it is advantageous that the carbon content notexceed about 0.05%, e.g., 0.03%, or less. However, in this regard,columbium when present, will combine with the carbon such that carboncontents up to 0.1% are satisfactory. Columbium also obviates thenecessity of solution treating weldments.

Particularly satisfactory hot workability characteristics are conferredby titanium and/ or aluminum. Contributing to the desideratum of lowcost is the fact that air melting techniques can be employed. Thusrecourse to more expensive processing is unnecessary. Titanium is alsouseful to stabilize nitrides, thereby preventing the occurrence ofporosity in ingots. Accordingly, it is preferred that at r least one,beneficially both, of these constituents be present in amounts of atleast 0.05%, advantageously at least 0.1% or'0.25%, and up to 0.5%.Appreciable amounts of these elements, however, e.g., 1.5% or 2%, arequite undesirable since the net etfect would be to subvert workabilitycharacteristics without benefit corrosionwise.

As indicated herein, air melting practice can be readily employed inpreparation of the alloys, although vacuum techniques can also be used.It might be mentioned, as will be appreciated by those skilled in theart, recovery of titanium and/or aluminum and/or calcium is usually not100%. Where it is desired that the alloys contain about 0.15% oftitanium or aluminum, about 0.25% of each should be added to the melt.Calcium, which can be incorporated in the form of a calcium-siliconaddition,

tested in the cold rolled and also in the annealed condition. Coldrolled specimens having a surface area of about square centimeters wereimmersed for about 72 hours in the 10% ferric chloride solution, rubberbands being wrapped thereabout to intentionally create crevices. Thistest is deemed equivalent to an extreme long-time exposure in sea waterand is described by M. A. Streicher in Journal of the ElectrochemicalSociety, vol. 103, pages 375390, No. 7, July 1956. Other cold rolledspecimens of the same alloys (same area) were annealed at about 2150 F.to 2200 F. for about one-half hour and tested in the annealed conditionand in the same manner as the cold rolled specimens. Nominalcompositions and data are given in Table I for both the cold rolled andthe annealed specimens. In addition to the percentages of the variousconstituents set forth in Table I, about 0.03% carbon (except Alloy 21),0.1% silicon, 0.15 manganese, and about 0.06% calcium (ascalcium-silicon) were added to the melts. Both titanium and aluminumwere used in preparing the alloys, about 0.25% of each being added.

TABLE I Weight loss in milligrams Cold rolled Ni, G M0, Other, Fe, Coldand percent percent percent percent percent rolled annealed should beadded in an amount of about two to three times that desired in the finalalloys. Ingots can be hot Worked from about 2200 F. to 2300 F. down toabout 1800 F. to 1600 F. Suitable annealing temperatures include about2000 F. to 2300 F., e.g., 2200" F. A final annealing temperature ofabout 2200" F. has been found satisfactory. In producing strip and thelike, the alloys can be hot rolled, annealed, pickled and cold rolled.Intermediate annealing between cold rolling stages can be carried outover the temperature range of 2000 F. to 2200" F. It is rather ironic tonote that it has been found difficult to pickle the alloys due to theexceptional corrosion resistance thereof.

In order to give those skilled in the art a better appreciation of theinvention, the following illustrative description and data are given:

A substantial number of alloys (Alloys 1 through 25, Table I) within theinvention were prepared using air melting techniques. Ingots were soakedat about 2300 F. and thereafter hot rolled to billets, the hot workingtemperature range being on the order of 1600 F. to 2300 F.

The hot rolled alloys were annealed at about 2150" F. to 2200 F. forabout one-half hour and were cold rolled to strip about inch thick (thehot rolled thickness was approximately inch). Corrosion tests wereconducted using an aggresive corrodent commonly used for test purposes,to wit, a 10% ferric chloride solution. In this regard, two differenttests were conducted. Specimens were In respect of the data in Table I,it is clear that Alloys 1 through 20 exhibited highly satisfactoryresistance to crevice corrosion. No pitting was observed. RegardingAll0y 21, this alloy nominally contained 0.15% carbon, the compositionotherwise being the same as for Alloys 2 and 3. While Alloy 21 isacceptable for castings and for applications concerning alloys in theannealed condition, it will be noted that the high carbon contentresulted, comparatively speaking, in quite a loss in crevice corrosion.As indicated above herein, it is much more desirable to maintain thecarbon content at a level not above 0.1% and advantageously less than0.05% or 0.03%. (It should be mentioned that alloys to be acceptable inthe 10% ferric chloride test described herein should not manifest a lossgreater than about 15 milligrams and advantageously not greater thanabout 10 milligrams, the optimum being a maximum loss of about 5milligrams.)

Some dilficulty was experienced in hot working Alloys 22 through 25,particularly Alloys 22 and 24 (which alloys contained only 20% nickel),although crevice corrosion resistance was good. Edge cracking was notedprimarily in respect of Alloys 22 and 24 and with such low nickelcontents, in combination with the molybdenum content of 10%,intermediate annealing would be necessary. However, as referred toherein and as illustrated by Alloys 7 and 13, nickel contents above 23%,to wit, 25%, resulted in good hot working characteristics.

Both cold rolled and annealed specimens of Alloys 3,

10, 11, 16 and 17 were exposed to sea water at ambient temperature (Howof 2 feet per second) at the renowned testing station at Harbor Island,N.C. Specimens to determine both crevice corrosion and stress corrosioncracking (U-bends) behavior were employed. Alloy 3 was exposed for aperiod of about 450 days, each of the others being exposed for about 300days (exposure continues in all cases), examinations being madeperiodically. Each of the specimens was free of any evidence of stresscorrosion cracking. A very slight and inconsequential amount of crevicecorrosion was Observed in connection with the cold rolled specimen ofAlloy 3 after 90 days, but this proved to be very incipient and did notprogress further. It is more than likely that machining prior toexposure was not perfect. In summary, the specimens behaved remarkablywell.

U-bend specimens of Alloys 2, 3, 10, ll, 12 and 16 were also exposed toboiling 42% magnesium chloride (154 C.) to determine stress corrosioncracking tendencies under the extremely severe conditions imposed bythis test (a test commonly used to determine stress corrosion crackingbehavior of the austenitic stainless steels).

ance essentially iron, when drawn to wire (94% reduction) had a tensilestrength of about 264,000 p.s.i. together with good bend and kinkductility. It is considered that tensile strengths on the order of up to300,000 p.s.i. are obtainable. Such strength levels would render alloyscontemplated herein particularly suitable for marine cable applications,although there are cable applications in which strength levels of about265,000 p.s.i. are quite satisfactory.

In addition to the foregoing, a number of alloys both within (numerals)and outside (letters) the invention were prepared and tested in the samemanner, except as otherwise noted, as the alloys of Table I. Thecompositions are given in Table II together with the test resultsobtained. Included are alloys conforming to various prior artcompositions and stainless steels AISI 310 and 316 which were producedcommercially. It should be emphasized that neither calcium nor titaniumor aluminum was added to Alloys EE, FF, HH through PP, 27, 28 and 29.Unless otherwise indicated, the alloys did not contain more than about0.03% carbon, 0.1% silicon, and 0.15% manganese.

TABLE II Ni, Cr, M0, Other, Fe, Cold Anpereent percent percent, percentpercent rolled nealed 4 Balance...

Nil

*Not Determined. Chemical analysis. Norm-Specimens of Alloys 30 through39 were cold worked to inch thick.

Alloys 2, 10, 11 and 12 were exposed in the annealed condition, Alloy 3in the cold rolled condition and Alloy 16 in both conditions. Alloys 2,3, and (each of which contained less than 35% of nickel plus cobalt)failed in 16, 8 and 12 days, respectively. No cracking was observed indays for the other specimens. As indicated herein, for optimumresistance to stress corrosion cracking in chloride media at least aboutnickel plus cobalt should be present in the alloys.

As an additional feature of the invention, alloys contemplated hereinexhibit high tensile strengths, e.g., about 250,000 p.s.i. and abovewhen cold drawn to wire. An alloy nominally containing 25% nickel, 20%chromium and 8% molybdenum, and less than 0.04% carbon, bal- Alloys AAthrough DD illustrate the inferior results characteristic of alloys withlow amounts of molybdenum (4%) and regardless of increase in the nickelcontent. Alloys EE and FF are representative of prior art alloys, freeof calcium and also titanium and aluminum. Again, crevice corrosionresistance was outstandingly poor. Alloy GG also manifested poorcorrosion resistance even though it contained calcium, titanium andaluminum. However, an alloy within the invention and of the same nominalcomposition (Alloy 26) but with 20% chromium reflected satisfactorycorrosion behavior. As indicated before herein, when the molybdenumcontent is less than about 6.5% the chromium content should be at leastabout 18%. Alloys GG and 26 illustrate this aspect. Alloy HH Wascharacterized by such poor hot workability that corrosion tests in thecold rolled and annealed conditions were not made. It will be noted thealloy contained high silicon 1.1%) and titanium (2%) contents as well asa high amount of silicon plus manganese (1.8%). In most marked contrastthereto are Alloys 15 and 9, alloys within the invention.

As indicated above herein, neither calcium nor titanium or aluminum wasadded to the melts of Alloys HH through PP and 27, 28 and 29. In thisregard, JJ through MM, 27, 28 and 29 (also Alloy 5) are of particularinterest. As will be observed, Alloys J], K and LL each exhibited poorcorrosion resistance whether in the cold rolled or annealed condition.Alloys 27, 28 and 29, however, were satisfactory in the annealedcondition and are thus within the invention for that reason. It is, ofcourse, interesting to compare Alloy 5 (which contained calcium and alsotitanium and aluminum) with Alloys 27, 28 and 29. It is thought thedifference in results is strikingly remarkable.

Alloys 30 through 39, 3 and QQ illustrate in a general manner alloybehavior as the nickel content is increased over the lower end of themolybdenum range. Note that Alloy 32 is an extremely marginalcomposition at best and only then in the annealed condition. With 18%chromium, an otherwise similar alloy (Alloy 31) exhibited considerablybetter corrosion resistance whereas, increasing the nickel content to30% as in Alloy QQ resulted in inferior resistance particularly in thecold rolled condition. As indicated before herein, improper correlationof the nickel and molybdenum contents can lead to poor results. Alloys3, 35 and 34 afford an interesting comparison with Alloy 39 concerningthe effect of increasing the chromium content (16.6% to 21%) as thepercentage of nickel increased (25% to 34%). The standard stainlesssteels AISI 310 and 316 as well as prior art Alloys NN and PP behavedpoorly in test.

Alloys contemplated within the invention are generally useful forvessels, boat hulls, and structures and components therefor employed in(or in the vicinity of) marine environments, including sea water and seaatmospheres. More specifically, the alloys are useful for pumps andparts therefor (including vanes and impellers), propellers, pipes,valves, fasteners, tubing in general including heat exchanger tubing andtube sheet, water boxes, seawater evaporators, including plate,shafting, marine hardware, e.g., chocks, cleats, pulleys, wroughtfittings, trim and fasteners, buoys, floating platforms, oil wellequipment, etc. Chemical plant equipment for handling of oxidizing acidsand salts thereof, containers and pressure vessels for the storage ortransportation of various corrosive chemicals are illustrative of otheruses for the alloys. Also, the alloys can be used in conventional millforms including sheet, strip, bar, rod, etc.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Under certain circumstances it may be permissible to usemagnesium together with or in place of calcium but it is much preferredto use the latter. Such modifications and variations are considered tobe within the purview and scope of the invention and appended claims.

We claim:

1. An iron-nickel-moly-bdenum-chromium alloy characterized by enhancedresistance to various corrosive chloride environments, said alloyconsisting essentially of about 20% to 40% nickel, about 6% to 12%molybdenum, the nickel and molybdenum being correlated to represent apoint falling within the area LFEDCL of the accompanying drawing, about14% to 21% chromium, the chromium being (a) at least about 18% when themolybdenum content is not greater than about 6.5% and (b) not greaterthan 20% when the molybdenum content is from about to 12%, up to 0.05carbon,

up to 0.15% calcium with the proviso that at least 0.001% of calcium ispresent when the molybdenum content is not greater than about 7.5%, atleast one metal selected from the group consisting of titanium in anamount up to about 0.7% and aluminum in an amount up to about 0.7%, upto about 12% cobalt, up to 0.5% silicon, up to 1% manganese, the sum ofany silicon and manganese not exceeding 1.25%, up to 1% columbium, up to1% vanadium, up to 1% copper, up to 1% tungsten, up to 2% tantalum andthe balance essentially iron.

2. An alloy as set forth in claim 1 containing at least 23% nickel andin which columbium, if present, does not exceed about 0.5%.

3. An alloy as set forth in claim 1 and containing about 0.001% to 0.15%calcium and from 6.5% to 8% molybdenum.

4. An iron-nickel-molybdenum-chromium alloy characterized by enhancedresistance to various corrosive chloride environments, said alloyconsisting essentially of about 20% to 40% nickel, about 6% to 12%molydenum, the nickel and molybdenum being correlated to represent apoint falling within the area ABCDEFA of the accompanying drawing, about14% to 21% chromium, the chromium being (a) at least about 18% when themolybdenum content is not greater than about 6.5 and (b) not greaterthan 20% when the molybdenum content is from about 10% to 12%, up to0.05% carbon, up to 0.15 calcium with the proviso that at least 0.001%of calcium is present when the molybdenum content is not greater thanabout 7.5%, at least one metal selected from the group consisting oftitanium in an amount up to about 0.7% and aluminum in an amount up toabout 0.7%, up to about 12% cobalt, up to 0.5% silicon, up to 1%manganese, the sum of any silicon and manganese not exceeding 1.25%, upto 1% columbium, up to 1% vanadium, up to 1% copper, up to 1% tungsten,up to 2% tantalum and the balance essentially iron.

5. An alloy as set forth in claim 4 wherein calcium is present in anamount of at least 0.001%.

6. An alloy as set forth in claim 4 and containing at least one metalfrom the group consisting of titanium and aluminum in an amount of 0.05to 0.6% of each.

7. An alloy as set forth in claim 4 in which silicon does not exceed0.25% and manganese does not exceed 0.5

8. An iron-nickel-molybdenum-chromium alloy consisting essentially offrom 23% to 30% nickel, from about 8% to about 10% molybdenum, thenickel and molybdenum being correlated to represent a point within thearea BGHJKB of the accompanying drawing, about 15% to about 20%chromium, up to 0.05% carbon, up to 0.15% calcium, at least one metalselected from the group consisting of titanium in an amount up to 0.7%and aluminum in an amount up to 0.7%, up to 12% cobalt, up to 0.5silicon, up to 1% manganese, the sum of the silicon plus manganese notexceeding 1.25%, up to 2% of columbium, up to 1% of vanadium, up to 1%copper, up to 1% tungsten, up to 2% tantalum and the balance essentiallyiron.

9. An alloy as set forth in claim 8 in which calcium is present in anamount of at least 0.01%.

10. An alloy as set forth in claim 8 in which silicon does not exceedabout 0.25% and manganese does not exceed about 0.5

11. An iron-nickel-molybdenum-chromium alloy which manifests excellentresistance to stress corrosion cracking and crevice corrosion inchloride media, said alloy consisting essentially of about 25% to 40%nickel, about 9.5% to 12% molybdenum, about 14% to 19% chromium, up to0.05% carbon, up to 0.15 calcium, at least one metal selected from thegroup consisting of titanium in an amount up to 0.7% and aluminum in anamount up to 0.7%, up to 0.5% silicon, up to 1% manganese, the sum ofthe silicon plus manganese being not greater than about 1.25%, up to 12%cobalt, the sum of the cobalt 1 1 plus nickel being at least about 35%,up to 2% columbium, up to 1% vanadium, up to 1% copper, up to 1%tungsten, up to 2% tantalum and the balance essentially iron.

References Cited UNITED STATES PATENTS Bieber 75171C Gibson 75-128.9

Bieber 75171H Franklin 75171A Abkowitz 75171H Heydt 75128.9

HYLAND BIZOT, Primary Examiner

